As is known, tests are currently being conducted on internal combustion engines, in which the suction and exhaust valves which selectively bring the combustion chamber of the engine into communication with the suction manifold and the exhaust manifold of the engine are actuated by electromagnetic actuators driven by an electronic control unit. This solution makes it possible to vary lift, opening time and moment of opening or closing of the valves as a function of the angular velocity of the crankshaft and of other operating parameters of the engine, thereby substantially increasing its performance.
Unfortunately, the internal combustion engines currently being tested have the major drawback that they require extremely powerful electromagnetic actuators whose weight and dimensions means that they are difficult to mount on the head of the engine. Moreover, the use of high power electromagnetic actuators makes it necessary to mount a large-dimension electrical generator, able to satisfy the massive demand for electricity, on the internal combustion engine, with prohibitive production costs.
The use of high power electromagnetic actuators is dictated by the need to exert axial forces of high value on the suction and exhaust valves. At specific operating moments of the engine, the electromagnetic actuator must be able to generate an axial force able to overcome not just the inertia of the valve but also the force exerted on the valve by the gases contained in the combustion chamber.
Considering, for instance, the instants preceding the opening of the exhaust valve, the combusted gases in the combustion chamber have a pressure of some 8 bar which act on the valve head and oppose its opening; if the electromagnetic actuator acting on the exhaust valve is therefore to be able to open the exhaust valve and bring the combustion chamber into communication with the exhaust manifold, it must produce a force equal to the product of the pressure on the head of the exhaust valve.
The value of the force exerted by the combusted gases on the exhaust valve is so high that in the internal combustion engines currently being tested, use is being made of electromagnetic actuators with powers that are much greater than 2 kW, a value which is in itself very high considering existing weight and space limits.